Up to now, attempts to incorporate a microphone unit and a speaker unit in a single casing have been made. Many of them are those which incorporate, in a single casing, a bone conduction microphone unit as a microphone, and an air vibration type speaker, such as a magnetic type one, ceramic type one, or dynamic type one, as a speaker (see FIG. 3). However, with this type of speaker and microphone containing type unit, the sound emitting port is opened, and thus it is difficult to provide a water-proof or dust-proof construction.
The present applicant has already proposed a bone conduction earphone with which a bone conduction microphone and a bone conduction speaker are incorporated in a single casing (Japanese Unexamined Patent Application Publication No. 2000-166959). This bone conduction earphone is composed of an insertion portion which is inserted into the external ear canal, being tightly contacted with the wall thereof, and a bone conduction speaker accommodating portion which is fixed to the insertion portion, the insertion portion being defined to be an earmold made of such a material as a relatively rigid plastic one. And, the bone conduction microphone is disposed being hermetically sealed in the rigid earmold, and the voice of the user is picked up by the bone conduction microphone from the external ear canal wall directly through the rigid earmold as a bone-conducted sound to be amplified and transmitted.
However, with this bone conduction earphone, the voice of the user is picked up by the bone conduction microphone as a bone-conducted sound through the rigid earmold which is inserted into the external ear canal, being tightly contacted with the wall thereof, and therefore, it is undeniable that someone can have an uncomfortable feeling (or a painful feeling). In the aforementioned patent document, it is stated that, in order to provide an improved feeling of wearing, the portion around the distal end of the earmold may be made of a soft material, however, this measure can be taken only for the portion around the distal end of the earmold.
In addition, with this bone conduction earphone, a bone-conducted sound is sensed by the rigid earmold portion, and the bone-conducted sound is transmitted directly from the earmold to the bone conduction microphone, with no consideration being given about the control of the acoustical characteristics (frequency characteristics) in that portion, and no special water-proof measure being taken.